Effect of simulated acid rain on the survival, mortality, behaviour and morphology of African mud catfish Clarias gariepinus (Burchell, 1822)

ABSTRACT. This study simulated acidic habitat for different life stages of Clarias gariepinus to know the effect on survival, mortality, morphology and behaviour. The fish were exposed to pHs 3, 4, 5, 6 and 8.01 (control) for 35 days. 100% mortality was recorded for all the life stages in pH 3, and 80, 62 and 36% of mortality of fingerlings, juveniles and adults respectively were recorded in pH 4. In pH 5, 30, 26 and 12% mortalities of fingerlings, juveniles and adults respectively were recorded and at pH 6 mortalities of fingerlings, juveniles and adults were 12, 10 and 4% respectively. Control pH mortalities were 10, 6 and 2% for fingerlings, juveniles and adults respectively. Mortality was due to lack of oxygen uptake, stress and circulatory collapse. All these elicited the behavioural responses and morphological abnormalities like erratic swimming, gasping, dark body colouration and lethargy. The study showed that different life stages of C. gariepinus tolerate different acidic pH waters, with high mortalities of the fingerlings, juveniles and adults in pHs 3, pH 4 is sub-lethal to fingerlings, juveniles and adult, pH 5 sub-lethal to fingerlings and sub-optimal for juveniles, and pH 6 optimal for all life stages.摘要：本研究针对革胡子鲶（Clarias gariepinus）的不同生活史阶段模拟酸性栖息环境，以探究其对受试对象存活率、死亡率、形态学特征与行为表现的影响。实验将受试鱼分别暴露于pH值为3、4、5、6及8.01（对照组）的水体中，持续35天。结果显示，pH3环境中所有生活史阶段的受试个体死亡率均达100%；pH4环境下，夏花鱼种、幼鱼和成鱼的死亡率分别为80%、62%与36%；pH5环境中，三类个体的死亡率依次为30%、26%与12%；pH6环境下，夏花鱼种、幼鱼和成鱼的死亡率分别为12%、10%与4%；对照组水体中，夏花鱼种、幼鱼和成鱼的死亡率则分别为10%、6%与2%。本次实验中受试鱼的死亡原因为摄氧障碍、应激反应与循环衰竭，上述胁迫均可引发行为响应与形态异常，具体表现为不规则游动、浮头呼吸、体色暗沉以及行动迟缓。本研究表明，革胡子鲶的不同生活史阶段对酸性水体的耐受能力存在显著差异：pH3环境下所有受试个体均出现高死亡率；pH4对夏花鱼种、幼鱼和成鱼均为亚致死环境；pH5对夏花鱼种具有亚致死效应，对幼鱼而言则为亚最优生长条件；pH6则为所有生活史阶段的最优pH环境。